Night mode is an automatic setting which takes advantage of the new wide-angle camera that's in the iPhone 11 and 11 Pro models. It's equipped with a larger sensor that is able to let in more light, allowing for brighter photos when the light is low.
macOS Catalina Now Available
Apple Accelerates Mac OS X 10.5.5 Seeding (9F17)
While difficult to predict when Apple will release this version to the public, accelerated releases with "no known issues" tend to be signs of an impending release.
Apple last updated Mac OS X with version 10.5.4 on June 30th, 2008. The next release will be a free update and is expected to incorporate over a hundred bug fixes.